Recently, the use of mobile terminals such as mobile phones is widely spread, which has made it important to reduce the size of the antenna used in mobile terminals in order to make these mobile terminals small. Especially, antennas which can completely be built inside the mobile terminals without protruding from the mobile terminals are demanded. Moreover, since a plurality of communication methods have spread for the mobile communication, the multi-band antennas are required, which are able to transmit and receive in a plurality of bands, as antennas for mobile terminals operate in various communication systems. Accordingly, various multi-band antennas which can be built inside mobile terminals are proposed (for example, refer to Japanese Patent Provisional Publication No. 2002-314326).
However, if the size of the antenna is reduced regardless of being a line antenna or planar one, it is difficult to maintain the required wide-band characteristics. Especially, adopting the method for reducing the size of the antenna by increasing the dielectric constant of the dielectric material surrounding the whole antenna makes it difficult to find appropriate design conditions which maintain the wide-band characteristics. Thus, the configuration of the prior art has a problem, for the use of the multi-band antenna which can be built inside a mobile terminal, that it is difficult to realize the reduction of the size of the antenna element with maintaining the wide-band characteristics.
Accordingly, the present invention is made to solve the problems like this and has an object of providing a compact antenna which is suitable to be built inside mobile terminals and able to realize both the reduction of the element size and the low profile with maintaining the wide-band characteristics, by adopting the configuration which is obtained by combining the dielectrics having three layered structure with a fed element and a grounded parasitic element.